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December 2005   1906-Level Temblor Would be Crippling
Study shows one-third of housing in S.F. might be destroyed;
similar survey urged for East Bay
SAN FRANCISCO — San Francisco city officials are reviving an earthquake study scrapped after early results showed a staggering third of the city's housing would be destroyed or uninhabitable, rendering a quarter-million people homeless, in a repeat of the infamous 1906 quake.

City officials now expect to carry the research past traditional estimates of quake damage to describing impacts on the functional health of the city and its people, then recommending ways of lessening those impacts.

No other U.S. city has performed such a detailed and scientifically rigorous analysis of earthquake effects, scientists said Tuesday in describing the study at the fall meeting of the American Geophysical Union. They said the East Bay, with equal or greater risk of a large earthquake in the next quarter-century, could benefit from a similar study.

"If anything, there should be a greater sense of urgency in Oakland," said Mary Lou Zoback, a seismologist for the U.S. Geological Survey in MenloPark. "You have 400,000 people living on or near a fault zone" with greater odds of rupture than the San Andreas fault that broke in the 1906 quake.

The most common method for evaluating seismic hazards is a computer model developed for the Federal Emergency Management Agency that treats homes uniformly as detached, single-family ranch houses with a set level of fragility for ground shaking.

The San Francisco study, performed by the Applied Technology Council in Redwood City, used homes more closely reflecting the mix of housing stock in the city, with more than half wooden structures predating World War II and 83 percent built before the imposition of modern seismic codes in the 1970s.

The study also accounted for large numbers of "soft story" houses and apartments that are considerably more at risk because of a less-supported, first-story garage.
Researchers also added in fires, which accounted for the majority of building losses in the 1906 quake. Violent ground shaking is expected to unleash more than 1,000 fires throughout the Bay Area, chiefly from broken natural-gas connections touched off by downed power lines and made harder to extinguish by severed water mains.
"You have the ignition, you have the fuel, and you have the inability to stop it," Zoback said Tuesday.

With those changes, the San Francisco study showed a repeat of the magnitude 7.9 earthquake of 1906 could trigger $40 billion in damages to buildings and $59 billion in total economic losses.

An overwhelming 70 percent of those losses would be homes wrecked or burned past habitation, as many as 130,000 houses and apartments in all. Most of those losses were projected in the city's western neighborhoods — from Sunset and Twin Peaks southward — where many homes are built on sand. A tenth of the losses came from liquefaction of those soils, and nearly another tenth came from fires.

When members of the city's Building Commission under former Mayor Willie Brown saw the early results, they protested that the study was getting too costly and not providing enough new information. In 2002, they voted to cancel it and issued a stop-work order. A Web site devoted to the study disappeared.

But recently the commission asked San Francisco's chief building inspector, Lawrence Kornfield, to resurrect and finish the study. In its final phases, the study will recommend ways of easing the harm of the Big One, possibly forcing the city to grapple with the seismic implications of its huge base of rent-controlled housing.

With more than 70 percent of the city's apartments in rent control, owners can't pass along the costs of seismic retrofitting. If their buildings were sufficiently damaged in an earthquake as to require demolition, they could rebuild free of rent controls and rent at ordinary market rates, potentially putting the city's poorest on the street.

The city's study will look at new policies and incentives to address such questions, as well as technological fixes.

Kornfield is working on one of his own. It is a kit of bolts and connectors for bolstering garage doors and soft-story buildings against full collapse, and Kornfield hopes the whole package will cost a few bucks at the local hardware store. He and engineers keep adding pieces to garage doors and shaking them until they break to see what works.

"We're just getting started on the project, but everyone's pretty optimistic," he said Tuesday evening. "It might work, and if it does, it will be a boon for people all around the state."

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Jointly by:
DRC Seismological Society of America EERI For Addtional Centennial Related Events:
An Affiliation of Earthquake Scientists, Engineers, and Emergency Managers.